Synergistic stabilizing compositions



Patented Nov. 3, 1953 r 2,657,933 SYNERGISIIC. STABILIZING GQMBGSIHONS Eugene F. Hill and Margaret Midli, sssigiior's "to Ethjgi Corporation, Flew. York, N. .,"a corporation: W'zii' No Drawing. Application March 18, 1952, Serial No. 217,336

2 iQYHliQQ li il tgs '4! 21. s e i imn. h :???1? 9i Brofecting only fuel, the r anic ma s. n ran y s sqtrtib de e 332s??? 2 I th i ll ffi l' hi it A p rtiw e ly Q i io relates 99 am rent 3 i' ifii fi i' fi t n I ir ltiQn oi attack by oxygen and the must c ter. uponth'aiitilghockfidditiile, asthf prolongation of the life of oggygien-sensitive 1 its 1 is rel 'v 7 1 'Furtheimore'fthis %??313115: Thi @PPliEEitiQ 5 3 Continuation of h a H fertil zati n erial 9 3 01 fi q ititi' i e i1 ""t e t r f Dace be: l9%9= ti iiieeq 9Q 5 t iels f iii rant se; i

gydi oea rlqgn iuel s to; internal combustion entimes that present ifi aiitoin otiiie ffilsf' sin s. be trqadly tla iiied nt? three e- 10, Hereteiere ti e PEQ Q P i i l fQr i i se ies attq di to the use r ich y a o ens" trimi the two intt t ii tls ip etiq i'qi S ar ignition ensues. inch $9 1 @irqei ar i nit sizes and fuels 9 wmpressi s i n lth ush each E L i wi ms d essentially o h d te itqas he in lii t er d in the memiif ttu ip pi s ahd Subsequent stora e an use arti ularl 1 the presenceof rnate! s i ers c nsittreb i r with ti m" tr mple. t pite w tqii fi ls" domain st a ht and tranthed thei h ic Olefins, napt henes and s me ermr i t While typical e ra t f els onta n me sr'p en i fins, In regent years fuels for cornpression ignitis engi es have ce e t d an i c a and na ral mer are, portion of cracked stocks, resulting in a higher I geptihie to ehsorp'tiofi"ofbziten'tvith cons-5 Qlefin torme t a d gq u t nc ini mis t i sil i iit eib ie i sf liihy's am ststepti ilit #9 sum q mai nhe efiect f 2 S @291 wi sv'ihe iiti e the deterioration of the fuel upon each type of A which render tlcljes rnqpig t f om n in tit r bu e u e li te se of 9.9. s ia s'fi 1i t fi i y b r1 ete it e 9n Q-Qwi each l- E'Qi l x nnie 9 Ox ge 'c i enis bm detriment at the 9 9. o gum i 'iue fq si n d b'r 1 st 1; iqsv 't spark ts n P iP SQ P E ES T nprm d s, o

" lude i ze ge sori d ara te But r el'ate deleterious ti on s imposed 0 fro A i.

f er fiiiethdii "rid diary pet rs 6 peretta f i? $39,39 s em "a d v 's Whi e he formation 9? t uii m ma rials in 90 1.: im gn t n en i e ful l nkrieres with th ormal p ei sm 9f th Iuel fi t rs d in t rs in s ch n i e In enera the h d ot bq s P ese t n au o m t a ni s r mqresii tepi l rade sm than the e pm ris n tirt e $1 9. @2 36 rf il fi o. H e r o a wm t and aircraft uels a see lin st ra t e m n bl nded wit etme h ad efmt us M s d it s rb 51. 61 b ess n m q ss i rihel mint bf inst We l t i t fi ished 1 s n e the ttirae lets 45 It s t er ie an b e t p 911 n ent on to pmis susceptible to some deterioration by contact vide meainsforp tis esteem?! substances with oxygen during the blending, storage and handling operations, with consequent formation of haze; loss of some ant-iknock "value, and lessened performance in the engine. This point'of attack is often overlooked and is ordinarily unimportant in automotive fuels, as the protective measures necessary for the base stock one usually more than sufiicient o protect the tetraet yllead. If hm ver, a stabi izin :iR lFQQi Qi? A ded H .o A b m erg oil suc a lubricatin acs zess 3 combustion spark, and compression ignition engines during the manufacturing, handling and storage of such fuels prior to their use without increasing the total amount of stabilizing additive. Likewise, it is an object of our invention to provide means for reducing the antioxidant requirement of unstable organic materials. A still further object of our invention is to provide hydrocarbon fuels containing tetraethyllead which do not deteriorate in contact with oxygen with the resultant formation of gum, haze and tetraethyllead oxidation products. It is also an object of our invention to provide fuels containing tetraethyllead in which there is essentially no loss in performance characteristics due to such deterioration of the tetraethyllead during blending, storage and handling. Likewise it is an object of our invention to provide means for preventing embrittlement, discoloration, loss of tensile strength and other harmful effects in elastomers during the milling, compounding, fabrication, storage, handling and use of such elastomer stocks. A further object of our invention is to provide means for protecting other perishable natural or synthetic organic materials from the adverse effects of contact with oxygen. Still further objects of our invention will appear from the description of our invention as hereinafter disclosed.

The above objects can be accomplished by practicing our invention which comprises adding to oxygen-sensitive organic materials a small proportion of a composition comprising hydroxy arylamino antioxidant materials and substances derived from. the class of esters of thioglycolic acid.

We have made the discovery that esters of thioglycolic acid themselves incapable of protecting organic materials from deterioration in the presence of oxygen, have the property of greatly increasing the effectiveness of hydroxyarylamino antioxidants. Such esters we refer to hereinafter as synergists. The synergistic thioglycolic esters of our invention include those wherein the esterifying radical is a hydrocarbon. Such radicals comprise aryl and aliphatic radicals. Thus, among the aryl esters we' contemplate, for example, phenyl, a-naphthyl, p-naphthyl, and other polynuclear aromatic radicals as well as substi-' tuted aryl radicals, such as tolyl, xylyl, ethylphenyl, cumyl, tetralin, methylnaphthyl and the like. Among the aliphatic thioglycolic esters which provide synergism in accordance with our invention we include alkyl esters such as methyl, propyl, isopropyl, n-butyl, sec.-butyl, isobutyl, the isomeric amyl, hexyl, heptyl, octyl, nonyl and the like up to and including about eighteen carbon atom alkyl radicals such as lauryl, stearyl and the like; alkenyl esters such as vinyl, allyl, methallyl, crotyl, phtyl, oleyl, undecenyl, and the like; cycloalkyl esters, such as cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl and the like; and aralkyl esters, such as benzyl, phenethyl, 2-phenylpentyl. and the like. The lower alkyl esters are among our preferred'synergists.

The hydroxy arylamino antioxidant components of our synergistic mixtures are well known, and include those employed in many antioxidant applications such as foodstuffs, fats, oils, greases, soaps, petroleum products, natural rubbers, synthetic hydrocarbon rubbers, such as the butyl, styrene and butadiene rubbers, as well as those of the chloroprene, thiokol, acrylonitrile, and silicone types, and plastics, for example, the vinyl, cellulosic, polyethylene types, etc. Typical hyvariety of test gasolines.

droxy arylamine antioxidants include p-aminophenol, N-n-butyl-p-aminophenyl, 1-amino4 hydroxy-naphthalene, N-isobutyl p aminophenol, N-isopropyl-p-aminophenol, l-N-butylamino-ahydroxynap-htha1ene, N-plienyl-p-aminophenol, N-cyclohexylamino-p-aminophenol, N- (p-hydroxyphenyl) p-phenylenediamine and the like. Where the hydroxy arylamino antioxidant can be considered as a naphthalene derivative we prefer to employ modifications wherein the hydroxy and amino groups are on the same aro matic nucleus. In general we prefer to employ the aminophenol type of antioxidant with our thioglycolic ester synergists.

We have found that the replacement of a portion ofthe hydroxy arylamine antioxidant of a stabilized composition with our synergistic thioglycolates, themselves incapable of providing oxygen stabilization, results in a stabilized composition which is remarkably resistant to attack by oxygen. Furthermore, to attain a specified degree of oxygen stability the required amount of our hydroxy arylamino-thioglycolic ester mixture is less than the required amount of the hydroxy arylamine antioxidant alone.

The absorption of oxygen by hydrocarbon fuels can be measured directly by the standard method of the American Society of Testing Materials for determination of the Oxidation Stability of Gasoline (Induction Period Method), ASI'M designation: D525-46, as fully described in Part III-A, ASIM Standards for 1946. According to this method the induction period is the period during which there is no absorption of oxygen by the test material as indicated by a drop in pressure, when placed in a testing bomb maintained at a temperature of C. with an initial pressure of 108 pounds per square inch gauge of oxygen. The Induction Period Increase (IPI) is the increase in the duration of this period caused by the addition of a protective substance, and is a direct measure of the protection afforded by such additive. Thus, the longer the IPI the more eflective is the stabilizer. On the contrary, certain substances exert a pro-oxidant effect in which a negative IPI is obtained, that is, the duration of the induction period, or period of no absorption of oxygen, is less than in the absence of the additive.

It is well known in the art of protecting gasoline from oxidation that the susceptibility to oxidation of gasoline varies significantly with different types of gasolines. Furthermore, it is likewise well known that the efiiciency of any antioxidant, and, therefore, the minimum concentration required, will vary greatly from gasoline to gasoline. Therefore, in order to show the general applicability of the compounds of our invention to the solution of this problem, and at the same time not present in detail the large amount of data so obtained, we have obtained representative Induction Period Increases with a The gasolines used in obtaining the data presented herein were all commercial blending stocks or finished gasolines and included the following types: An average-response gasoline containing 20 per cent olefins and 14 per cent aromatics, the remainder being parafiins and naphthenes; a gasoline containing approximately 38 per cent olefins, 33 per cent aromatics, and the remainder parafiins and naphthenes; a gasoline containing 18 per cent olefins and 24 per cent aromatics; a high-sulfur gasoline containing 0.21 per cent sulfur; and a gaso- '5- line containing 28 per cent olefins-and '18 per cent aromatics with medium sulfur content.

In general, the synergistic component of our novel antioxidant compositions is. ineffective as an antioxidant. When tested by the above-mentioned ASTM method we obtain results ranging from zero IPI or insignificant values, such as to minutes, to negative values of IPI.

That is, the synergistic component may actually.

be an oxidizing material, or a pro-oxidant. Typical of such results is that. obtained with isopropyl thioglycolate, which at a level of 6 milligrams per 100 milliliters of test gasoline actually reduced the induction period of the untreated fuel by 70 minutes.

Other thioglycolate esters of our invention which do not exhibit an antioxidant effect when employed alone in gasoline include methyl thioglycolate, n-butyl thioglycolate, isobutyl thioglycolate, cyclohexyl thioglycolate, phenyl thioglycolate, amyl thioglycolate, benzyl thioglycolate, allyl thioglycolate, lauryl thioglycolate, n-dod'ecyl thioglycolate, and a-naphthylthioglycolate.

The eifectiveness of typical synergistic mix-. tures of our invention is shown by-adding to the test gasoline a total concentration of 6 milligrams of the synergistic mixture per 100 milliliters of gasoline, and comparing the increase in the induction period of the test gasoline obtained with that obtained with the arylamine antioxidant alone at the same total concentration of 6 milligrams per 100 milliliters of gasoline. Thus, employing a mixture comprising 2.0 milligrams of isopropyl thioglycolate and 4.0 milligrams of Nn-butyI-p-aminophenol per 100 milliliters of gasoline an IPI of 405 minutes was obtained, while in a similar determination using 6.0 milligrams of N-n-butyl-p-aminophenol an IPI of only 340 minutes was obtained. Thus, replacing one-third of the antioxidant with a pro-oxidant actually increased the efiectiveness of the re- -maining antioxidant by thirty-three per cent.

Similar results were obtained with a mixture comprising 33 per cent isopropyl thioglycolate and 67 per cent N-isobutyl-p-aminophenol at a total concentration of 6 milligrams per 100 milliliters of gasoline. The IPI of the so-treated fuel was 410 minutes, while using 6 milligrams of N- isobutyl-p-aminophenol alone per 100 milliliters of gasoline produced an IPI of only 335 minutes. Like results are obtained by employing equal parts of N-n-butyl-p-aminophenol and ethyl thioglycolate, 33 per cent cyclohexyl thioglycolate and 67 per cent N-cyclohexyl-p-aminophenol, per cent phenyl thioglycolate and 75 per cent 1- (methylamino) -4-hydroxy naphthalene, equal parts of allyl thioglycolate and N-( i-hydroxyphenyl) -p-phenylenediamine, and per cent stearyl thioglycolate and 70 per cent N-isopropylp-aminophenol.

We have demonstrated the efiiciency of the synergistic mixtures of our invention in preventing undue formation of gum in automotive gasolines by storing such gasolines containing them for long periods, and determining from time to time the gum content of the fuel. The quantity of gum so-formed was compared with that formed in the presence of known antioxidants and in the untreated gasoline. Two commercial motor gasolines, consisting of 2'7 and 38 per cent olefins and initially containing 0.6 and 0.8 milligrams of gum per 100 milliliters, were employed. For each demonstration duplicate amber quart bottles were filled with one pint of the gasoline with or without an additive. The bottles were stoppered and stored in the dark at a temperature of 110 F. Every four weeks the bottles and their contents were cooled to room temperature-and the stoppers were removed for two hours to permit access to the air. Every 8 weeks. a sample of the fuel mixture was removed and the dissolved gum therein was determined by the so-called air-jet evaporation method, ASTM designation: D38l- 46, fully described in ASTM Standards for 1946, Part III-A. Thus, by incorporating our thioglycolate esters, which by themselves are not antioxidants, into gasoline containing materials known to be antioxidants, a substantial reduction in the amount of gum formed during storage was obtained compared to the gasoline containing the antioxidant alone. In this comparsion, our synergists were used in addition to known antioxidants, and resulted in improved storage stability of the fuel. As a further embodiment we have replaced part of the antioxidant material with our synergists, thereby obtaining equivalent protection but utilizing for the purpose a smalle quantity of the antioxidant.

Our synergists likewise afiord protection to hydrocarbon solutions of tctraethyllead as shown by a series of tests in which hot-acid isooctane containing 4.6 milliliters of tetraethylleadper gallon was heated at a temperature of Gin a stainless steel bomb with oxygen added to an initial pressure of 100 pounds per square inch gauge. Under these conditions the pressure in a bomb containing only isooctane and a tetraethyllead antiknock mixture underwent a sharp drop after four hours, indicating absorption of oxygen by the fuel mixture. Various amounts of known antioxidants and our synergistic mixtures are thereupon added until it is determined at what minimum concentration the pressure in the bomb does not drop during a period of 16 hours at a temperature of 100 C. By using our mixtures, nearly a two-fold ir crease in efiectiveness can be obtained, compared to the hydroxy arylamine antioxidant alone at a reduced concentration of total additive.

A further class of organic substances sensitive to oxygen comprises the elastomers, natural and synthetic. To illustrate the utility of the synergistic mixturesof our invention in protecting such substances a natural rubber compounded into a typical tire-tread formula is convenient. One requisite of such stocks is that the desirable properties incorporated therein by careful selection of the compounding ingredients and cure time shall be maintained during extended periods of storage or use in the presence of oxygen. Comparison of various rubber stocks is best carried out on stocks initially having the same state of cure. The most reliable means for determining the state of cure is by the T-50 test, ASTM designation: D599-40T, described in the ASTM standards for 1946, Part III-B. This test measures the temperature at which a test piece recovers its elasticity when it is stretched at room temperature, frozen at a sufiiciently low tempera ture to cause it to lose its elastic properties, and then gradually warmed. In practice the temperature noted-is that at which the sample recovers to 50 per cent of the original elongation and is, therefore, referred to as the T-5O value. In these tests stocks for testing and comparison are cured for a time suilicient to have a T-50 value of +l 0., so that a valid comparison of the properties can be made. The accelerated aging is conducted by the procedure of ASTM designation:..D572-42, described in the ASTM i saiii tidsi rot-19346; has; for t end es; 5 5 I I 57s i a; 1 w fe 96 1 hours at l a temperature of,

ounds er square inch I I mg: the following; compositiQi 1 rial to, be

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' i sp cific i herein by: way of: examples a r e 3 mp o d y I i I i I j We lhavejdisclo sed gs number,

be for nvention are-determined I ng-i' These proherties: are, EGompared mix r i' n" and after agi 'bber stock protected 'i by E the aryl amin o dantf alone, Land finallywith a stock not protected was inhibitor; B othro these proper ties were determined by means 9 f=ASTMdesignatiQniz ectional: area required to breaigj I hp men, while the :uitiinate elongation I I elongation at the moment; 0f; rupture? 91 f I I specimen: r A fiecrese; in the values for ether hes'e properties-upcniaging represents ecrease n; th I visefz'ilness" df the article fabricated them;

rorni. so that :thedeg-ree to which theseproperties eoif o stabilized; I n ipjart by the: specific; alr v 3 nd v and 100 parts lie; ester gtoi, lOGIpa-rts'by med; Y

by. weight of thioglycfo weight; of 5 hydroxy aryiam bod nts of our invention and illustrated se'v erali r m is whereby p ot c n a b afie I I I taiiiins the advanta es; :PQ jSibleI i eeti ve n; inhibiting; oxidation ;i e organic imlateriai con n QAi 'syherg i I v in inhi itin gzfoxiclatio I I I I I v v nicf imateriaisgcensisgtf g essenti between about; f and: 5190 parts: gbyf weight hi siy l nd a ou 1 9 parsh we fs' I ninoph enolcomposition c nic material tending :to diet onsisting essential i are' irtaineidzis: a direl t me s r 9 he i il twio rescue of x e and "he t'c ant 'o of the protective substance. When the following gi 5 k i g i i i fg typical mixtures of the synergists of our invention inhibit such d giiig q g. i are so-tested as much as a 100 per cent increase ture consistin in the tensile strength and a per cent increase in mi i y 0 t a 1.- in the ultimate elongation is obtained: 33 per 2% e 0x1 an an an es er 0 log yco 1c g isopmpghfliioglycolate' 67 cent 0 2 The compvtion of claim 1 wh ein said IOXY-a-IIELP y amine; 25 per cen anaph hyl r x l a inshinstrainers 2; than i z gg g g h g fi acid is isopropyl thioglycolate J gyco a e, per cen u y -am1noydroxy naphthalene; and 33 per cent ethyl thio- 50 g g gggsg g g gg g i gfjt fgfi glycolate cent droxyphenyl)-p-phenylen diamine and sa d es- The quantities of the mixtures of our invention tor of thiocl colic A i H 1 61 incorporated in the materials to be stabilized b y ap y yare not critical and depend largely upon the type 6 h com nsmon of 01 1 b of material being stabilized and the conditions hyd'rmy gi i 2.33 TL under h the exposure to oxygen occurs For am no-5-hydroxynaphthalene and said ester of example, with gasolines, tetraethyllead, mineral 11661 Celia ack'i 0 i hex W I 1 1 i oils, lubricating oils, diesel fuels, and similar ma- 7 ig com is. Y a terials the mixtures of our invention are prefp05} Ion c-agn Wlerem Sam erably employed in concentrations between the allfirlamlne f i s N nbl-ltyl l-jlimits of approximately 0.1 and 15 milligrams per l ggg zg g 1 5: estel of blloglycohc acld 100 milliliters of material to be stabilized. For X petrilgumahfimcarbon fuel for internal g gg g fligfi g g sg gg z 2 321; igig gfii combustion engines normally subject to deterigreases somewhat larger amounts 0% the stabiomfionIm the presence of Oxygen containing as I a principal antioxidant ingredient a synergistic 5 Q Qur mVenI 1911 are PreferIred and can be mixture consisting essentially of a hydroxy aryll l'flt d' IRE n such ma l We mm -Y amine antioxidant and an ester of thioglycolic b tw n p m e y 01 an 2 Parts O yn acid, said ester being present in amount between SW1 m t PQ 0 a t 9 9 4 3 ti? about 30 and parts per 100 parts of said For pla tic q fis e c W n e q m y hydroxy arylarr ine and said syneristic niixmie between ab t n 1 pa t of y e gi c pr se tm m n be ween ut cite 1'5 miiii-i m xijill P 0 P 2 Q f lQ E Q l ifi fllgrams per 100 'milliliters of said hydrocarbon Thus, our mixtures can be satisfactorily employed f l;

75 '9. The composition of claim 8 wherein said in a wide range of concentrations, and we do not a r st ict d, to the. I I I 1 si shmi o w lbe I 1 determined; in: partsby th nature; ref; the mate I I I a was nsitive to, attack by cm: I d v our synergistic mixtures; as othffi iinjethods of; 1 i .7 v V Iracticin'fiouninenti withv th sa roper ies determines r a n ld B n I I p g V eriiorate; n the hydroxy arylamine antioxidant is N-n-butyl-paminophenol and said ester of thioglycolic acid is isopropyl thioglycolate.

10. The composition of claim 8 wherein said hydroxy arylamine antioxidant is N-isobutyl-paminophenol and said ester of thioglycolic acid is isopropyl thioglycolate.

11. The composition of claim 8 wherein said hydroxy arylamine antioxidant is N-n-butyl-paminophenol and said ester of thioglycolic acid is ethyl thioglycolate.

12. A composition consisting essentially of at least one hydrocarbon that normally tends to deteriorate in the presence of oxygen and an efiective amount of a synergistic antioxidant mixture of a hydroxy arylamine antioxidant and an ester of thioglycolic acid, said ester being present in amount between about 30 and 100 parts per 100 parts of said hydroxy arylamine antioxidant by weight and said synergistic mixture being present between about 0.1 and 2 parts by weight per 100 parts of said elastomer.

13. The composition of claim 12 wherein said ester is isopropyl thioglycolate and said hydroxy arylamine is 4-hydroxya-naphthylamine.

14. The composition of claim 12 wherein said ester is a-naphthyl thioglycolate and said hydroxy arylamine is N-(phydroxyphenyl) -pphenylenediamine.

15. The composition of claim 12 wherein said ester is ethyl thioglycolate and said hydroxy arylamine is N-n-butyl-p-aminophenol.

16. The composition of claim 12 wherein said ester is cyclohexylthioglycolate and said hydroxy arylamine is N-butyl-1-amino-5-hydroxynaphthalene.

EUGENE F. HILL. MARGARET L. OSIP.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,227,517 Starkweather et al. Jan. 7, 1941 2,606,169 Roney Apr. 5, 1952 

2. A SYNERGISTIC ANTIOXIDANT COMPOSITION EFFECTIVE IN INHIBITING OXIDATION IN OXYGEN-SENSITIVE ORGANIC MATERIALS CONSISTING ESSENTIALLY OF BETWEEN ABOUT 30 AND 100 PARTS BY WEIGHT OF ALKYL THIOGLYCOLATE AND ABOUT 100 PARTS BY WEIGHT OF AN AMINOPHENOL. 